Structure of ${}^{107}\mathrm{Sn}$ studied through single-neutron knockout reactions

The neutron-deficient nucleus ${}^{107}\mathrm{Sn}$ has been studied by using the one-neutron knockout reaction. By measuring the decay $\gamma$ rays and momentum distributions of reaction residues, the spins of the ground, $5/2^{+}$, and first-excited, $7/2^{+}$, states of ${}^{107}\mathrm{Sn}$ have been assigned by comparisons to eikonal-model reaction calculations. Limits on the inclusive and exclusive cross sections have been measured and transitions due to neutron removals from below the $N=50$ closed shell have been observed. New excited states up to $5.5$ MeV in ${}^{107}\mathrm{Sn}$ have been identified.

Figure 1

Particle-identification spectrum for the reaction products of the ${}^{108}\mathrm{Sn}$ beam passing through the ${}^9\mathrm{Be}$ target. The energy loss measured in the ion chamber is plotted versus the ion's flight time with the requirements of $\gamma$-particle (top) and only particle (bottom) coincidence. For the latter case, the particle single trigger was downscaled by a factor of 10. Several other isotopes have been produced and identified via $\gamma$ spectroscopy, such as ${}^{106}\mathrm{In}$ and ${}^{104}\mathrm{Cd}$.

Figure 2

Spectrum of $\gamma$ rays following neutron removal from a ${}^{108}\mathrm{Sn}$ beam, gated on ${}^{107}\mathrm{Sn}$ residual nuclei. The blue (solid) line shows a fit to the data; in light blue (dotted) the geant4 simulation of the CAESAR detector for the observed $\gamma$ transitions; the exponential background is shown as a red (dashed) line.

Figure 3

Momentum distributions of the ${}^{107}\mathrm{Sn}$ reaction residues in the first-excited state. The data are overlaid to eikonal model reaction calculations for neutron removal from a $2d_{5/2}$ orbital (blue solid) and a $1g_{7/2}$ orbital (red dashed).

Figure 4

CAESAR calorimeter distribution between 25 and 8425 keV. The 1222–1280 keV (club) and 1349–1370 keV (spade) multiplets are marked. The top-right inset shows an example of a singles spectrum gated on the calorimeter energy in the $5400–5600$ keV range. Two distinct peaks above the background events are visible around 1280 and 4200 keV.

Figure 5

CAESAR calorimeter distribution between 900 and 1700 keV. The 1222–1280 keV (club) and 1349–1370 keV (spade) multiplets are marked. Here, the data (black solid line) and the geant4 simulation (red dashed line) are compared: the expected and the measured resolution for the two peaks of interest are in good agreement.

Figure 6

Proposed level scheme for ${}^{107}\mathrm{Sn}$. New highly excited states (red dashed lines) have been observed cascading directly into the ground and excited states (red arrows). The experimental resolution of these new levels is estimated to be about 100 keV.